1. Field of the Invention
The present invention relates: generally to biological conductivity testing cells possessing a substantially cylindrical structure; more particularly to biological conductivity testing cells possessing a substantially cylindrical structure with two opposed Pt alloy electrodes disposed upon either end; and most specifically to biological conductivity testing cells possessing a substantially cylindrical structure with two opposed Pt alloy electrodes disposed upon either end intended for passage of a weak alternating current therethrough for the obtainment of impedance measurements.
2. Prior Art
Biological conductivity testing cells possessing a substantially cylindrical structure with two opposed Pt alloy electrodes disposed upon either end intended for passage of a weak alternating current therethrough are considered to be well known. With regard to the present innovation the prior art is considered to be restricted to simple deposition of Pt alloy upon equivalent areas with regard to either end including interior, exterior, and end surfaces.
FIG. 1 depicts a conventional conductivity testing cell 10 made of a glass cylinder 11 and two opposed electrodes 12 between which a weak alternating current in passed through a biological sample held therein for measuring changes in impedance associated with metabolic activity inclusive of cell division and genetic replication. FIG. 2 depicts in detail an end of the conventional conductivity testing cell 10 depicted in FIG. 1 inclusive of a portion of the glass cylinder 11 and an electrode 12 with exposed interior and exterior surfaces 21, 20 resulting from the simple deposition of the Pt alloy which are both offset with respect to the adjacent exposed glass interior and exterior surfaces 15, 17, and necessarily present an exposed edge 22 of the electrode 12 which is subject to shear. It is further seen that the covered glass interior and exterior surfaces 15, 17 under the electrode 12 are the same as the adjacent exposed glass surfaces 15, 17.
Conventional conductivity testing cells 10 made of a glass cylinder 11 possessing two opposed electrodes 12 between which a weak alternating current is passed through a biological sample held therein must be autoclaved between tests in order to assure sterility prior to introduction of a new biological sample. Repeated autoclaving results in separation of the Pt alloy deposition comprising the electrodes 12 from the underlying glass interior and exterior surfaces 15, 17. Serious deterioration of the electrode 12 resulting from shear during autoclaving is typically experienced after only three cycles of using the testing cell 10.
The electrodes 12 must be Pt alloy because platinum possesses unique characteristics with regard to electro-chemical activity: platinum, alone among all the elements, acts as a pure catalyst for electro-chemical activity without loss of material and without other undesired activity. It is noted that the portions of the electrodes 12 disposed interiorly in conventional conductivity testing cells 10 comprised of a glass cylinder 11 as depicted in FIG. 1 extend inwardly much further than the portions of the electrodes 12 disposed exteriorly. This is because the exterior portion makes electrical contact with a metal conductor while the interior portion facilitates the conductance of electrical current through a water based biological sample and a greater surface area is required to support the conductance of the electrical current across the interface with this inherently less conductive medium.
With a current cost of approximately twice that of gold platinum is considered relatively expensive. Platinum has many industrial uses including laboratory glassware and catalytic converters necessary to NOx reduction from internal combustion engine exhaust. It is not anticipated that the cost of platinum will be greatly reduced in near future owing to anticipated demand. While the amount of platinum in the Pt alloy deposition upon a conventional biological conductivity testing cell is measured in grams a degraded electrode 12 cannot be repaired without return of the testing cell for complete removal and redeposition of the Pt alloy and conductivity test cells 10 are hence routinely discarded after deterioration of one of the electrodes 12.
Therefore, the entire cost of the conductivity test cell 10 must be amortized over an average of approximately three tests, including the cost of manufacturing the glass cylinder 11, the platinum in the Pt alloy deposition, the process of deposition, transportation, and all other expenses associated with getting a product to market. While the cost of replacing a conductivity test cell 10 after an average of three tests may be acceptable in research it is recognized that this cost is inhibitive of clinical usage wherein millions of tests annually are anticipated. A need is hence discerned for a means of increasing the number of tests a biological conductivity test cell 10 can be utilized prior to deterioration of the electrodes 12.
The encompassing object of the principles relating to the present invention is a biological conductivity testing cell with a platinum alloy electrode upon each of two opposed ends of a glass cylinder which is relatively unaffected by autoclaving.
A first auxiliary object of the principles relating to the present invention is the provision of a chemically pure surface upon end surfaces of a glass cylinder intended for deposition of platinum alloy thereby eliminating contamination.
A second auxiliary object of the principles relating to the present invention is the provision of a uniform surface roughness upon end surfaces of a glass cylinder intended for deposition of platinum alloy for resisting shear.
A third auxiliary object of the principles relating to the present invention is the provision of platinum alloy upon the two opposed ends of a glass cylinder wholly within the overall cylindrical cell dimensions thereby eliminating all exposed edges of the deposition.
A fourth auxiliary object of the principles relating to the present invention is the provision of radially and axially uniform etching upon end surfaces of a glass cylinder intended for deposition of platinum alloy for resisting shear.
A fifth auxiliary object of the principles relating to the present invention is the provision of evenly spaced grooves annular upon end surfaces of a glass cylinder intended for deposition of platinum alloy for resisting shear.
Ancillary objects of the principles relating to the present invention include the preservation of desired electrical characteristics of the electrodes comprised of the deposition of platinum alloy upon the end surfaces of a glass cylinder in use as a biological conductivity testing cell for the measurement of impedance of a weak alternating current passed through a biological sample contained therein and the utilization of a greater interior surface area relative the exterior surface area of each end of the glass cylinder for deposition of platinum alloy thereupon.
In achievement of the above stated objectives it is suggested that removal of glass surface material by abrasion from the end surface areas of a glass cylinder intended for deposition of platinum alloy prior to deposition be effected. If the entire surface area intended for deposition thereupon is abraded with a chemically inert abrading material immediately prior to deposition of the platinum alloy a chemically pure, virgin, surface is obtained and all potential contaminates which could later cause separation eliminated.
Utilization of an appropriate abrasion also achieves a uniform surface roughness also provides resistance to shear. With a uniform removal of glass surface material from the entire area intended for platinum deposition to a depth equivalent to the thickness of the coating deposited thereafter a substantially continuous exterior surface of electrode and exposed glass surface is obtained and exposed edges of electrode are avoided and separation from shear acting upon exposed edges eliminated.
Selective removal of glass surface material in an annulus located at the edge of the intended platinum deposition will also, regardless of other removal of glass material from the other areas of the deposition surface, ensure elimination of exposed electrode edges and separation from shear acting upon the same. Annular grooves located at consistent axial intervals with regard to both ends of the glass cylinder in the deposition area will provide physical resistance to axial shear displacement of the platinum deposition without adversely affecting the electrical characteristics of the biological conductivity testing cell.
Similarly, axial grooves located at consistent radial intervals with regard to the glass cylinder in the deposition area will provide physical resistance to radial shear displacement of the platinum deposition without adversely affecting the electrical characteristics of the biological conductivity testing cell. And a helical diamond pattern of grooves located at consistent intervals in the deposition area will provide physical resistance to both axial and radial shear forces without adversely affecting the electrical characteristics of the biological conductivity testing cell. These grooves can be in addition to a uniform removal of glass surface material.
It is recommended in all cases that removal of glass surface material from the two end areas of the glass cylinder intended for deposition of platinum alloy be effected with appropriate abrasion using an inert abrading material. The grain size is determinative of the resulting roughness of the surface abraded. Regardless of the specific type of glass utilized, and borosilicate glasses are considered satisfactory, silicon carbide grinding wheels are suggested for abrading any grooves.
A small diameter silicon carbide cylinder is suggested for effecting a uniform removal of glass surface material from the concave interior cylindrical surfaces and a large diameter silicon carbide wheel is suggested for the convex exterior surfaces. The axes of the glass and silicon carbide cylinders are in both cases parallel. Abrasive cloth is also suggested for the convex exterior surfaces and the end surfaces, which are flat, are preferably abraded with an opposed flat surface which could be moving, as presented by a belt, or stationary, with linear or rotary displacement of the glass cylinder in compression against the flat abrading surface.
Use of conventional vapor deposition techniques and conventional platinum alloys including iridium, osmium, rhodium, rhenium, and ruthenium are recommended although it is noted that the last two, at 5.5% and 4% the conductivity of copper, which compare with 16% for pure platinum, are low compared with the other alloys. A platinum iridium alloy of between 5 to 30 percent iridium is preferred for superior conductivity.
Other aspects regarding preferred manners of making and using an embodiment in accordance with the principles relating to the present invention may be appreciated in a reading of the detailed description further below, particularly if made with reference to the drawings attached hereto, and described briefly directly below.